Abstract: Frequency diverse array (FDA) radar has drawn a remarkable amount of attention owing to its particular range-dependent beampattern. In order to solve the problem of robust beamforming in frequency diverse radar, the frequency diverse subaperturing multiple-input multiple-output (FDS-MIMO) radar array signal model is established and the analytical of the weight vector decomposition is derived based on the equivalent carrier frequency. Then, a novel decomposition and iterative robust adaptive beamforming algorithm is proposed. Futhermore, the idea of applying co-prime frequency offsets along two directions of the planer array is presented to mitigate the periodic signal-to-interference plus noise ratio (SINR) loss which results from the range-dependent beampatern grating lobe. Simulation results show that the proposed methods can mitigate the periodic SINR loss, and has the advantages in computational burden, requiement of snapshots and robustness under the condition of steerig vector mismatch compared with the conventional algorithms.